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| United States Patent |
5,260,393
|
|
Arcella
, et al.
|
November 9, 1993
|
Vinylidene fluoride based fluoroelastomeric copolymers modified with
perfluoroalkylvinylether
Abstract
Fluoroelastic copolymers, suitable for the manufacture of O-rings,
comprising by weight:
48-65% of VDF units
21-36% of HFP units
3-9% of PAVE units
0-17% of TFE units
| Inventors:
|
Arcella; Vincenzo (Novara, IT);
Brinati; Giulio (Milan, IT);
Albano; Margherita (Milan, IT);
Minutillo; Anna (Milan, IT);
Chiodini; Graziella (Saronno, IT)
|
| Assignee:
|
Ausimont S.p.A. (Milan, IT)
|
| Appl. No.:
|
015266 |
| Filed:
|
February 8, 1993 |
Foreign Application Priority Data
| Jul 24, 1991[IT] | MI 91 A 002040 |
| Current U.S. Class: |
526/247; 526/249; 526/254; 526/255 |
| Intern'l Class: |
C08F 016/24 |
| Field of Search: |
526/247,249,254,255
|
References Cited
U.S. Patent Documents
| 4123603 | Oct., 1978 | Stewart, Jr. | 526/254.
|
| 4745165 | May., 1988 | Arcella et al. | 526/250.
|
| Foreign Patent Documents |
| 407937 | Jan., 1991 | EP | 526/247.
|
Primary Examiner: Schofer; Joseph L.
Assistant Examiner: Sarofim; N.
Attorney, Agent or Firm: Cave; Bryan
Parent Case Text
This is a continuation of U.S. application Ser. No. 07/744,778, filed Aug.
14, 1991, now abandoned which is incorporated by reference herein.
Claims
We claim:
1. An ionically vulcanizable fluoroelastomeric copolymer exhibiting
improved compression set characteristics suitable for the production of
O-rings, consisting essentially of the following non-brominated monomeric
units:
(a) 48-65% by weight of vinylidene fluoride (VDF);
(b) 21-36% by weight of hexafluoropropene (HFP);
(c) 3-9% by weight of perfluoroalkylvinylether (PAVE); and
(d) 0-17% by weight of tetrafluoroethylene (TFE); wherein the sum of the
HFP and PAVE contents is at least 27 weight %.
2. The fluoroelastomeric copolymer of claim 1, wherein the percentage by
weight of component (c) is 4-8%.
3. The fluoroelastomeric copolymer of claim 1, wherein the percentages by
weight of components (a), (c) and (d) are:
(a) 60.5-64%,
(c) 5-8%; and
(d) 0-8%;
and the sum of the HFP and PAVE contents is 30-33% by weight.
4. The ionically vulcanizable fluoroelastomeric copolymer of claim 1,
wherein component (c) is selected from the group consisting of
perfluoromethylvinylether, perfluorethylvinylether and
perfluoropropylvinylether.
Description
THE PRIOR ART
The present invention concerns novel fluoroelastomeric copolymers, suitable
for the manufacture of 0.rings, based on monomeric units being derived
from vinylidene fluoride (VDF), exafluoropropene (HFP), and if desired
tetrafluoroethylene (TFE), which are ionically vulcanizable, show good
elastomeric characteristics at both high and low temperatures and give a
good processability, in terms of releasability from the mold after
vulcanization.
Known fluoroelastomeric copolymers consist of VDF and HFP, which are useful
for preparing 0.rings. Such copolymers show good properties at high
temperatures, but poor properties at low temperatures.
U.S. Pat. No. 4,123,603 and Italian Patent Application No. 41,003 A/90 in
the name of the Applicant, describe terpolymers consisting of units of
VDF, HFP and TFE at concentrations within a very limited range, which are
ionically vulcanizable, give a satisfactory combination of properties at
low and high temperatures, and at the same time possess good
processability, especially regarding releasability from molds after
vulcanization, for which they are particularly suitable for the
manufacture of O-rings.
Said terpolymers nevertheless have the disadvantage of a very specific and
limited monomeric composition, that precludes their use in other
applications.
In the above mentioned terpolymers the optimization of the monomeric
compositions gives an improvement of TR 10 (ASTM D1329) not superior to
about 3.degree. C. with respect to the above described copolymers
consisting of VDF and HFP units.
It is known that fluoroelastomers showing better low temperature
characteristics are those based on VDF, PAVE and possibly TFE units,
containing small amounts of bromine containing olefins, or bromo
alkylvinylethers, vulcanizable by free radicals with peroxides and
crosslinking agents.
Nevertheless products obtained by using this type of crosslinking show poor
compression set characteristics unsuitable for the production of O-rings.
Ionic vulcanization, which has the general advantage of giving rise to
easily processable products showing better compression set values with
respect to those from the free radical system, cannot be used, for the
above mentioned fluoroelastomers.
In fact it results in polymer degradation and worsening of some properties,
among which is the compression set at high temperatures.
With regard to this, the publication by W. W. Schmiegel "Crosslinking of
Elastomeric Vinylidene Fluoride Copolymers with Nucleophiles" in "Die
Angewandte Makromolekulare Chemie", No. 76/77/1979 can be cited.
French Patent No. 2,259,849 discloses ionically vulcanizable
fluoroelastomeric copolymers, consisting of VDF, HFP, TFE and PAVE units,
the latter of which is between 17 and 30% by weight based on the total
monomers.
Finally, French Patent No. 2,347,389 discloses analogous fluoroelastomeric
copolymers in which the content of PAVE units is between 10 and 17% by
weight.
The fluoroelastomers of these patents show better characteristics in terms
of TR 10 and compression set at low temperatures. Nevertheless the value
of their compression set at high temperatures is poor. From tests carried
out by the Applicant, copolymers having the monomeric composition
exemplified in the two French Patents, show at 200.degree. C. a
compression set of above 24%. Furthermore, during the vulcanization
carried out by ionic methods, the copolymers tend to become porous or to
display bubbles on the surface due to the formation of volatile
decomposition products, such as F.sub.2 CO and HF, and foul the
vulcanization molds (fouling). For these reasons, the polymers described
in said patents are not suitable for use in the manufacture of O-rings.
THE PRESENT INVENTION
Fluoroelastomeric copolymers have now unexpectedly been found and form the
object of the present invention, which comprise VDF, HFP, PAVE units and
possibly contain also TFE units, wherein the PAVE units are comprised in
quantities between 3 and 9% by weight, preferably between 4 and 8% by
weight, based on the total monomeric units, which can be vulcanized by
ionic methods without the above mentioned drawbacks, do not show fouling
problems, and possess surprising low temperature characteristics, in
particular in terms of values of TR 10, while maintaining sufficiently low
compression set values at high temperatures, less than 20%. In particular,
said copolymers are able to satisfy commercial specifications such as
"Military Specification (MIL-R-83248B)", which requires a maximum value of
20% for the compression set on O-rings at 200.degree. C. for 70 hours.
The copolymers which are the object of the present invention are
characterized by the following composition of monomeric units by weight:
______________________________________
VDF 48-65%
HFP 18-36%
PAVE 3-9%
TFE 0-17%
______________________________________
the sum of HFP +PAVE being a minimum of 27%.
Said copolymers are particularly suitable for the production of O-rings.
With respect to the terpolymers described in U.S. Pat. No. 4,123,603 and
Italian Patent Application No. 41,003 A/90, cited above, the copolymers of
the present invention exhibit, at substantially equivalent contents of
other monomers, and in particular VDF, a surpisingly improved low
temperature performance.
Furthermore the present products show the advantage of being able to be
used for articles requiring chemical resistance toward polar fluids, such
as for example methanol, when VDF is sufficiently low, e.g. less than 55%
by weight, preferably about 50% by weight.
This combination of properties cannot be obtained simultaneously with the
prior art copolymers.
Particularly preferred for their optimum combination of low and high
temperatures characteristics, as well as processability, are the
copolymers having the following composition by weight of monomeric units:
______________________________________
VDF 60.5-64%
HFP + PAVE 30-33%
TFE 0-8%
PAVE 5-8%
______________________________________
One further embodiment of the present invention consists in the use, for
the manufacture of O-rings, of copolymers characterized by the following
composition of monomeric units by weight:
______________________________________
VDF 48-64%
HFP 18-36%
PAVE 3-12%, preferably 3-9%
TFE 0-17%
______________________________________
the minimum value of HFP+PAVE being as indicated above.
The fluoroelastomeric copolymers of the present invention can be prepared
by copolymerization of monomers by known methods, such as, for instance,
those described in Kirk Othmer, Encyclopaedia of Chemical Technology, vol.
8, pages 500 and ff., 1979. In particular, polymerization in bulk, in
organic solvent solution and in emulsion or suspension in water can be
used as the polymerization methods.
Radical polymerization initiators which can be used are for example organic
peroxides, such as ammonium or potassium persulphates, redox systems such
as persulphate/bisulphite and iron persulphate, organic peroxides such as
benzoyl peroxide, dicumylperoxide, diisopropylperoxydicarbonate,
diethylhexyl. peroxydicarbonate, etc..
Preferably the preparation is carried out in an aqueous emulsion. Any type
of emulsifier, fluorinated or partially fluorinated, or mixtures thereof
with hydrogenated emulsifiers, can be used in the process of the
invention; an example of emulsifier is given by fluorinated carboxylic
acids.
Chain transfer agents which can be used are for example ethyl acetate,
diethyl malonate; chain transfer agents containing iodine and/or bromine
can also be use, such as for instance compounds having the general formula
Rf(I).sub.x (Br).sub.y (Rf=a perfluorinated hydrocarbon radical containing
from 1 to 8 carbon atoms, x, y=integers comprised between 0 and 2, with at
least x or y=1 and x+y.ltoreq.2).
Furthermore alkaline or alkaline earth metal iodides and/or bromides can be
used as chain transfer agents, as described in European Patent Application
No. 407,937.
Polymerization temperatures are comprised between 25.degree. C. and
150.degree. C. and operating pressures between 8 and 80 atmospheres.
The perfluoroalkylvinylethers (PAVE) to be used in the preparation of the
copolymers of this invention are those containing alkyl groups having 1-3
carbon atoms, such as perfluoromethylvinylether (PMVE),
perfluoroethylvinylether (PEVE), and perfluoropropylvinylether (PPVE).
PMVE is preferred.
The preparation of the copolymers in accordance with the present invention
can be advantageously carried out by polymerization in an aqueous
suspension in the presence of a microemulsion formed by one or more
perfluorooxyalkylenes and water, as described in European Patent
Application Nos. 247,379 and 250,767.
Vulcanization systems usable for the polymers of the invention are well
known and consist of a crosslinking agent and a vulcanization accelerator.
Usable crosslinking agents are for example those described in U.S. Pat.
Nos. 4,259,463, 3,876,654, 4,233,421 and may include aromatic and
aliphatic polyhydroxylic compounds.
Representative examples of the aromatic class are di-, tri- and
tetrahydroxybenzene, -naphthalene, -anthracene and bisphenol derivatives.
Preferred are aromatic compounds which include 4,4-thiodiphenol
isopropylene-bis(4-hidroxybenzene) (i.e. Bisphenol A) and
hexafluoroisopropylene-bis (4-hydroxybenzene) (i.e. Bisphenol AF), which
are described in U.S. Pat. No. 4,233,421.
Compounds which can be used as vulcanization accelerators are known and are
described, for example, in U.S. Pat. Nos. 3,655,727, 3,712,877, 3,857,807,
3,686,143, 3,933,732, 3,876,654, 4,233,421, 4,259,463, and in European
Patent Application Nos. 0,182,299 and 0,120,462. Preferred are the
compounds from the class of phosphonium and aminophosphonium quaternary
salts described in U.S. Pat. Nos. 3,876,654 and 4,259,463.
In addition to O-rings, the copolymers of the present invention can also be
used for preparing articles exhibiting a good compression set at high
temperatures.
The following examples serve to illustrate the object of the present
invention without having a limitative value.
The values of releasability of the plaques from the aluminum foil after
treatment in press at 170.degree. C. for 10 minutes are indicated with A
when the release is good, and with B when it is mediocre.
EXAMPLE 1
A 5 l reactor equipped with a stirrer operating at 630
3,500 g of water are charged into the reactor under vacuum and the reactor
is then brought to pressure using a monomeric mixture having the following
molar composition:
______________________________________
VDF 48%
HFP 39%
PMVE (perfluoromethylvinylether)
13%
______________________________________
The operating temperature is 85.degree. C. and the pressure 19 relative
bar.
Thereafter are added, in sequence:
4.2 g ammonium persulphate (PSA), dissolved in water.
6.4 g ethyl acetate as chain transfer agent, 3.2 g of which at 5% monomer
conversion and the remainder subdivided into 4 additions of 0.8 g each,
executed at 24%, 43%, 62% and 81% conversion, respectively.
The pressure is maintained constant during the polymerization, by feeding
the monomers at the following molar ratios:
______________________________________
VDF 78.5%
HFP 17.5%
PMVE 4.0%
______________________________________
After 66 minutes, 1,413 g of the polymer are obtained. The reactor is
cooled, the emulsion discharged and coagulated by adding an aqueous
solution of aluminum sulphate.
The polymer is isolated, washed in water and dried in an air circulating
oven at 60.degree. C. for 24 hours.
Table reports the data relative to the polymer composition, the value of
the glass transition temperature T.sub.g, and of the Mooney viscosity.
Table 2 reports data concerning the formulation used for the polymer
vulcanization, the characteristics of such formulation, as well as the
characteristics of the vulcanized polymer, after post-vulcanization in the
oven at 230.degree. C. for 24 hours. The vulcanization of the polymer has
been carried out in press at 170.degree. C. for 10 minutes.
EXAMPLE 2
A reactor as in Example 1 is used.
The reactor is brought to pressure using a monomeric mixture having the
following molar composition:
______________________________________
VDF 47%
HFP 45%
PMVE 7%
______________________________________
The operating temperature is 85.degree. C. and the pressure 19 relative
bar.
Feeding of PSA and ethyl acetate are carried out as in Example 1.
Pressure is maintained constant during polymerization by feeding a
monomeric mixture of the following molar composition:
______________________________________
VDF 78.5%
HFP 19.5%
PMVE 2.0%
______________________________________
After 65minutes of polymerization, 1,450 g of the polymer are obtained.
Tables 1 and 2 report the data concerning the characteristics of the
polymer obtained, the vulcanizing formulation and the vulcanized product.
EXAMPLE 3 (COMPARATIVE)
Operating conditions are as in Example 1, with the exception that the
reactor pressure is attained using a monomeric mixture having the
following molar composition:
______________________________________
VDF 53.5%
HFP 46.5%
______________________________________
The pressure is maintained constant during polymerization by feeding a
monomer mixture having the following molar composition:
______________________________________
VDF 78.5%
HFP 21.5%
______________________________________
After 70 minutes of polymerization 1,560 g of polymer have been obtained.
Tables 1 and 2 report the data concerning the characteristics of the
obtained polymer, the vulcanizing formulation and the vulcanized product.
EXAMPLE 4
A 10 l reactor equipped with a stirrer operating at 545 r.p.m. was used.
6,500 g of water are charged into the reactor under vacuum and the reactor
is then brought to pressure using a monomeric mixture having the following
molar composition:
______________________________________
VDF 61.0%
HFP 28.0%
PMVE 9.0
TFE 2.0
______________________________________
The operating temperature is 85.degree. C. and the pressure 19 relative
bar.
Thereafter are added, in sequence:
7.8 g of PSA dissolved in water.
14.8 g of ethyl acetate, 7.4 g of which at 5% monomer conversion and the
remainder subdivided into 4 additions of 1.85 g each, executed at 24%,
43%, 62% and 81% conversion, respectively.
The pressure is maintained constant during the polymerization, by feeding
the monomers at the following molar ratios:
______________________________________
VDF 81.0%
HFP 12.0%
PMVE 4.0%
TFE 3.0%.
______________________________________
After 52 minutes reaction time, 2,750 g of the polymer are obtained.
Tables 3 and 4 report the characteristics of said polymer, of the
vulcanizing formulation and of the vulcanized product.
EXAMPLE 5 (COMPARATIVE)
Operating conditions are as in Example 4, with the exception that the
reactor is brought to pressure using a monomer mixture having the
following molar composition:
______________________________________
VDF 59%
HFP 36%
TFE 5%
______________________________________
Pressure is maintained constant during polymerization by feeding a
monomeric mixture of the following molar composition:
______________________________________
VDF 77.2%
HFP 16.5%
TFE 6.3%
______________________________________
After 62 minutes of reaction 2,800 g of the polymer are obtained.
Tables 3 and 4 report the characteristics of the polymer, the vulcanizing
formulation and the vulcanized product.
EXAMPLE 6
Operating conditions are as in Example 1, with the exception that in this
case the pressure in the reactor is attained using a monomer mixture
having the following molar composition:
______________________________________
VDF 57%
HFP 30%
PMVE 10%
TFE 4%
______________________________________
Pressure is maintained constant during polymerization by feeding a
monomeric mixture of the following molar composition:
______________________________________
VDF 78.5%
HFP 14.0%
PMVE 3.5%
TFE 4.0
______________________________________
Tables 5 and 6 report data concerning the characteristics of the obtained
polymer, the vulcanizing formulation and the vulcanized product.
EXAMPLE 7 (COMPARATIVE)
Operating conditions are as in Example 1, with the exception that in this
case the pressure in the reactor is attained using a monomer mixture
having the following molar composition:
______________________________________
VDF 38%
HFP 53%
TFE 9%
______________________________________
Pressure is maintained constant during polymerization by feeding a
monomeric mixture of the following molar composition:
______________________________________
VDF 70.0%
HFP 19.0%
TFE 11.0
______________________________________
After 65 minutes of polymerization, 1,550 g of the polymer are obtained.
Tables 5 and 6 report data concerning the characteristics of the obtained
polymer obtained, the vulcanizing formulation and the vulcanized product.
TABLE 1
______________________________________
Example
1 2 3
______________________________________
Polymer Composition (% weight)
VDF 58.3 58.6 60.7
HFP 32.8 36.9 39.3
PMVE 8.9 4.5 0.0
TFE 0 0 0
Mooney (ML (1 + 10) 121.degree. C.
52 58 50
Viscosity
T.sub.g
(.degree.C.) -27 -26 -23
(DSC)
______________________________________
TABLE 2
______________________________________
Example
1 2 3
______________________________________
Composition of Vulcanizing Formulation:
Polymer 100 100 100
M1 4 4 4
M2 1.5 1.5 1.5
MgO DE 3 3 3
Ca(OH).sub.2 6 6 6
MT Black 30 30 30
Formulation Characteristics:
ODR 177.degree. C. ARC .+-.3 (ASTM D 2084-81)
ML (pounds .times.
16 16 16
inch)
MH (pounds .times.
116 118 121
inch)
T.sub.s2 (s) 147 135 132
T'.sub.90 (s) 243 234 228
Crosslinking Yield
(MH-ML) 100 102 108
Characteristics of the Product
(Vulcanized in Press at 170.degree. C. for 10 min
and Post-Vulcanized at 230.degree. C. for 24 hrs)
(ASTM D412-83)
M 100 (MPa) 6.6 6.7 7
C.R. (MPa) 14.7 15.1 15.9
A.R. (%) 176 174 178
Shore A 73 74 73
(ASTM D 2240-81)
TR Test (ASTM D1329)
TR 10% (.degree.C.)
-20 -19 -17
TR 30% (.degree.C.)
-16 -15.0 -13
TR 50% (.degree.C.)
- 13 -12.4 -10.9
Compression Set
(200.degree. C. for 70 hrs) (ASTM D1414-78)
O-RING
23.degree. C. for 70 hrs
(%) 18 15 14
(ASTM D395/B)
0.degree. C. for 70 hrs
(%) 11 11 11
(ASTM D395/B)
DISC (12.5 .times.-29 mm):
Reading after 30 min
(%) 5.8 4.5 3.9
at 23.degree. C.
Reading after 24 hrs
(%) 2.8 2.2 2
at 23.degree. C.
Plaque Release from Aluminum Foil
(after treatment in
A A A
press at 170.degree. C. for
10 min)
______________________________________
M1: Master 50% elastomer/50% Bisphenol AF
M2: Master 70% elastomer/30% Diphenylbenzyl, Ndiethylphosphonium chloride
TABLE 3
______________________________________
Example
4 5
______________________________________
Polymer Composition (% weight)
VDF 61.0 61.4
HFP 23.0 30.8
PMVE 8.0 0.0
TFE 8.0 7.8
Mooney Viscosity
(ML (1 + 10) 121.degree. C.)
38 36
T.sub.g (DSC)
(.degree.C.) -34.4 -29.0
______________________________________
TABLE 4
______________________________________
Example
4 5
______________________________________
Composition of Vulcanizing Formulation:
Polymer 100 100
M1 4 4
M2 1.5 1.5
MgO DE 3 3
Ca(OH).sub.2 6 6
MT Black 30 30
Formulation Characteristics:
ODR 177.degree. C. ARC .+-.3 (ASTM D 2084-81)
ML (pounds .times. inch)
12 13
MH (pounds .times. inch)
98 100
T.sub.s2 (s) 129 117
T'.sub.90 (s) 193 186
Crosslinking Yield
(MH-ML) 86 87
Characteristics of the Product
(Vulcanized in Press at 170.degree. C. for 10 min
and Post-Vulcanized at 230.degree. C. for 24 hrs)
(ASTM D412-83)
M 100 (MPa) 5.2 5.7
C.R. (MPa) 15.0 15.4
A.R. (%) 196 186
Shore A 70 70
(ASTM D2240-81)
Test TR (ASTM D1329)
TR 10% (.degree.C.) -25 -19
TR 30% (.degree.C.) -21 -15
TR 50% (.degree.C.) -18 -12
Compression Set
200.degree. C. for 70 hrs (ASTM D1414-78)
O-RING
23.degree. C. for 70 hrs
(%) 18 15
(ASTM D395/B)
0.degree. C. for 70 hrs
(%) 20 18
(ASTM D395/B)
Disc (12.5 .times. 29 mm):
Reading after 30 min
(%) 18 17
at 23.degree. C.
Reading after 24 hrs
(%) 11 9
at 23.degree. C.
Plaque Release from Aluminum Foil
(after treatment in press at 170.degree. C. for
A A
10 min)
______________________________________
M1: Master 50% elastomer/50% Bisphenol AF
M2: Master 70% elastomer/30% Diphenylbenzyl, Ndiethylphosphonium chloride
TABLE 5
______________________________________
Example
6 7
______________________________________
Polymer Composition (% weight)
VDF 53.5 51.3
HFP 26.7 36.1
PMVE 8.0 0.0
TFE 11.8 12.6
Mooney Viscosity
(ML (1 + 10) 121.degree. C.)
55 62
T.sub.g (DSC)
(.degree.C.) -31.7 -21.6
______________________________________
TABLE 6
______________________________________
Example
6 7
______________________________________
Composition of Vulcanizing Formulation:
Polymer 100 100
M1 4 4
M2 1.5 1.5
MgO DE 3 3
Ca(OH).sub.2 6 6
MT Black 30 30
Formulation Characteristics:
ODR 177.degree. C. ARC .+-.3 (ASTM D 2084-81)
ML (pounds .times. inch)
14 15
MH (pounds .times. inch)
111 99
T.sub.g2 (s) 135 162
T'.sub.90 (s) 255 300
Crosslinking Yield
(MH-ML) 97 84
Characteristics of the Product
(Vulcanized in Press at 170.degree. C. for 10 min)
and Post-Vulcanized at 230.degree. C. for 24 hrs)
(ASTM D412-83)
M 100 (MPa) 5.7 5.2
C.R. (MPa) 14.9 15.2
A.R. (%) 209 234
Shore A 72 73
(ASTM D2240-81)
Test TR (ASTM D1329)
TR 10% (.degree.C.) -22 -15.8
TR 30% (.degree.C.) -18 -12
TR 50% (.degree.C.) -15.5 -9.8
Compression Set
(200.degree. C. for 70 hrs) ASTM D1414-78)
O-RING
23.degree. C. for 70 hrs
(%) 19 19
(ASTM D395/B)
0.degree. C. for 70 hrs
(%) 14 12
(ASTM D395/B)
Disc (12.5 .times. 29 mm):
Reading after 30 min
(%) 11 10
at 23.degree. C.
Reading after 24 hrs
(%) 5 3
at 23.degree. C.
Plaque Release from Aluminum Foil
(after treatment in press at 170.degree. C. for
A A
10 min)
______________________________________
M1: Master 50% elastomer/50% Bisphenol AF
M2: Master 70% elastomer/30% Diphenylbenzyl, Ndiethylphosphonium chloride
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